Wireless communication standards continue to evolve. For example, in the cellular context, standards are currently evolving from third generation (3G) standards to fourth generation (4G) standards. The 3G standards include GSM and UMTS standards promulgated by an organization known as the 3G Partnership Project (3GPP) and CDMA2000 standards such as High Rate Packet Data (HRPD) promulgated by an organization referred to as 3GPP2. The 4G standards currently under development by 3GPP are generally referred to as Long Term Evolution (LTE) standards. The 3GPP and 3GPP2 standards documents, including, for example, 3GPP Technical Specification (TS) 36.213, Group Radio Access Network, Evolved Universal Terrestrial Radio Access (E-UTRA), Physical Layer Procedures, Release 9, V9.0.1, December 2009, are incorporated by reference herein in their entirety.
LTE networks make use of an Internet protocol (IP) based packet core referred to as Evolved Packet Core (EPC). User equipment (UE) communicates with the EPC via an access network that includes an enhanced base station referred to as an evolved NodeB (eNodeB). The uplink between the UE and the eNodeB uses SC-FDMA (Single Carrier FDMA). Uplink communications from multiple UEs within a given cell should be received orthogonally at the eNodeB in order to minimize interference. The desired orthogonal reception is achieved using a closed-loop control system in which the eNodeB estimates the uplink timing of the UEs by detecting a prime length Zadoff-Chu sequence in a random access preamble (PRACH) received from each UE and then based on this estimated timing sends periodic timing advance instructions to the UEs. Additional details of this conventional timing adjustment process can be found in, for example, the above-cited 3GPP TS 36.213, and also in “LTE—The UMTS Long Term Evolution,” S. Sesia et al., eds., ISBN 9780470697160, Wiley InterScience, 2009.
The performance of the above-described conventional closed-loop control system generally improves with decreasing cell size. This is because smaller cells will typically have more orthogonal sequences available and therefore a better detection probability for any particular sequence.